Surgical stapling and cutting instruments have been used in the prior art to simultaneously make a longitudinal incision in tissue and apply lines of staples on opposing sides of the incision. Such instruments commonly include a pair of cooperating jaw members that, if the instrument is intended for endoscopic or laparoscopic applications, are capable of passing through a cannula passageway. One of the jaw members receives a staple cartridge having at least two laterally spaced rows of staples. The other jaw member defines an anvil having staple-forming pockets aligned with the rows of staples in the cartridge. The instrument includes a plurality of reciprocating wedges which, when driven distally, pass through openings in the staple cartridge and engage drivers supporting the staples to effect the firing of the staples toward the anvil.
An example of a surgical stapler suitable for endoscopic applications is described in U.S. Pat. No. 5,465,895, which advantageously provides distinct closing and firing actions. Thereby, a clinician is able to close the jaw members upon tissue to position the tissue prior to firing. Once the clinician has determined that the jaw members are properly gripping tissue, the clinician can then fire the surgical stapler. Firing places all of the staples into the tissue and advances a knife to sever the tissue. The simultaneous severing and stapling avoids complications that may arise when performing such actions sequentially with different surgical tools that respectively only sever or staple.
It is often advantageous to build an end effector for the surgical stapler that is reusable. For instance, one patient may need a series of severing and stapling operations. Replacing an entire end effector for each operation tends to be economically inefficient. This is especially true if the end effector is built for strength and reliability over repeated operations. To that end, staple cartridges are fitted into the end effector prior to each operation of the surgical stapler. Thus, a much smaller amount of the surgical staples is discarded after each use.
While the staple cartridge provides numerous advantages, it is desirable to prevent inadvertent firing of the instrument when an unfired staple cartridge is not present. Otherwise, the severing of tissue may occur without the staples to minimize bleeding. It is particularly desirable that preventing such inadvertent firing be accomplished in a reliable way that is not subject to an intervening malfunction. Moreover, for ease of manufacturing and assembly, it is further desirable that the lockout features be accomplished with a minimum number of components.
Lockout mechanisms based upon vertical movement of the knife are known and particularly well-suited for non-articulating endocutter designs in which the end effector is located at the end of a generally rigid shaft. The shaft enables insertion to a desired depth and rotation about the longitudinal axis of the shaft, thereby enabling the end effector to be positioned to a degree. A U.S. Pat. No. 5,878,938 to Bittner et al. discloses a locking mechanism, or lockout, that uses a leaf spring to automatically lift a knife of the cartridge after a firing operation, thus locking the instrument so that subsequent firing operations are prevented. U.S. Pat. No. 5,673,842, also to Bittner et al., teaches a locking mechanism using an elongated member that automatically rotates from a first position to a second position as the instrument is fired. With the locking arm in the second position, the knife is free to translate upwardly and lock the instrument.
Such lockout mechanisms may be less suited for use in articulating surgical stapling and cutting instrument designs in which the end effector is located at the end of a shaft incorporating an articulating mechanism. A U.S. Pat. No. 6,786,382 to Hoffman discloses a surgical stapling and severing instrument incorporating an articulation mechanism for coupling the shaft to the end effector. Firing of the staples and severing of tissue is effected by a flexible firing mechanism extending through the articulation mechanism that is capable of transferring large loads therethrough in both flexed or unflexed states. Despite the greater clinical flexibility generally afforded by articulating instrument designs, the geometry of the firing mechanism and/or the physical forces present while the firing mechanism is in a flexed state may sufficiently restrict its vertical movement such that the above-described lockout mechanisms cannot be effectively employed.
Consequently, a significant need exists for improved lockout mechanisms for use in articulating surgical stapling and severing instruments that prevent inadvertent firing (i.e., severing and stapling) when a staple cartridge is spent or otherwise not present in an unfired position.